One of the more common "issues" with
the Discovery 2 is the SLS - "Self Leveling suspension". Probably the most
common failure is that of leaking Air springs that are in place on the rear
axle where traditional coils are fitted. Quite often what happens is the
car will "drop" at the back overnight or when parked for long periods of
time. This is 99% of the time due to leaking air springs. They generally
leak where the spring "rolls over" itself at the lower piston, or after a
few years the rubber can crack at the same point and leak as well.

Normally even if the car does drop,
when the vehicle is restarted the rear suspension will pump back up to
normal ride height again, this is off course assuming the compressor assy
itself has not failed.

The compressors are generally reliable
units, but what can "kill" them early is leaking air springs that are
ignored, so the compressor has to work for a lot longer periods than its
designed to do to keep the vehicle level due to the leak, so this can burn
them out prematurely.

It was for this reason, that upon
noticing my car had sagged at the back one or 2 times over a couple of
weeks, I wasted no time and
got on with replacing the Air springs. I could def see that it was the
rear left spring that was leaking, but both sides tend to drop as it tries
to sit level. You can replace just the spring that is faulty, but I would
HIGHLY RECOMMEND you replace them BOTH at the same time so you know where
you are.

What can be done to investigate the
problem, is raise the vehicle with the offroad height switch and give the
bags a soaking with a soapy water spray solution, this will find any leaks
if they are obvious, but the bags can sometimes self seal as they roll
over the lower piston, this is why the car may drop randomly and with no
pattern to it. If it drops every / other day, then honestly don't bother
looking for leaks, just replace them. Replacing the air springs is really
quite a simple task to do as long as you have some axle stands, a trolley
jack and can use a spanner.

First of all just "loosen" the
rear wheel nuts on both rear wheels, then you need to get the car up and
supported on the chassis, the best place to do this is next to where the
rear radius arms connect to the chassis rails either side. Before jacking
and "if" you have one, engage the CDL and chock BOTH front wheels with
either bricks or blocks of wood.

Lift the car so it just starts to take
the weight of the rear axle, then put the axle stands in each side and
lower it slowly onto them.

Then get 2 jacks, either trolley or
bottle, I used my trolley jack and the vehicle bottle jack, lift and
support the rear axle so the rear wheels are just of the floor, and then
remove both rear wheels,

Next we have to somehow de-pressurize
the Air springs, below you can see there is a 10mm connection union on top
of each air spring, but because of where it is, its difficult to get a
spanner in there to undo them, so its easier to let the air pressure out
at the compressor end.

Under the vehicle level with the front
passenger seat (UK car) the suspension compressor assy is housed in a
small plastic box bolted to the outside of the left hand chassis rail.
It has 2 "Zeus" quick release fasteners that once undone
allow you to lift of the cover. Once the cover is off, a the front of the
compressor assy you will see 3 unions / air pipes. We are ONLY interested
in the outside 2 pipes NOT the middle one

They are also 10mm in size, one at a
time, undo them slowly and allow the air pressure to escape, once the
"hissing" stops, you can simply check by squeezing each air spring, if its
fully depressurized it will squash easily. Take care not to get any dirt
on the pipe unions and into the compressor assy itself

Now we need to remove the air spring
itself, the tope is held by 2 spring retaining clips, and depending on how
old your vehicle is or if they have been replaced before will depend on
the condition of the spring clips. I had bought new ones just incase, but
to be honest my originals were "ok" to re-use. You can see them before you
start the job anyway, so worth checking to see if you need to order some
new ones.

I found its easiest to just remove
them carefully with a flat bladed screwdriver, try not to loose them if
you don't have new ones ready !! Picture below for ref the spring clips
(air spring out)

Once they are off, you can then
partially collapse the air spring down from the top, this will make it
easier to get a spanner on to undo the top air pipe connection, be careful
not to "stretch" the air pipe whilst doing this as there is not a lot of
slack in it.

Once the pipe is off, collapse the air
spring fully down so it clears the top seat. The bottom is simply hooked
in place. If you look at your new springs, this will be easy to see. So
rotate the whole thing from the bottom 90* and it will simply lift out.

Below you can see the bottom fixing on
the axle. Once the air spring is out, give the top and bottom seats a good
clean / brush down of any dirt and rust etc

Here is a comparison of a new one to
the old one. Now, depending on where you buy your new air springs from,
will depend on how they connect back to the vehicle system. Land Rover
charge TWICE as much for new air springs than any other spare parts
retailers, Land Rover specialists and even Ebay is cheaper as well. My new
springs have a "push" fit connector as opposed to the brass union "o" ring
type found on the original springs.

I'm not sure what type you would get
even if you bought them from Land Rover, it maybe just a more modern way
of connecting them up, who knows ?? My replacement springs were genuine
Dunlop items, you can see the top connection difference in the picture
below

Now because of the push fit connector,
you have to remove the brass fitting from the vehicle pipe work. Get a NEW
sharp stanley knife, slide the brass union back up the pipe to reveal the
olive on the pipe, then cut the pipe squarely, directly behind the olive
to keep as much length as possible. You can cut the pipe either before or
after re-fitting the new spring.

Now its time to refit the new spring,
simply collapse the new spring down, and without "twisting" it, refit the
bottom of the spring to the axle by rotating it 90*. Make sure you fit the
new spring so the pipe outlet is on the correct side. If the spring wont
reach the top fitting, or is to long, you can simply move the axle up or
down using the 2 jacks so you can engage it and refit the locking spring
clips on the top 2 studs.

Once its in place, push the air
pipes FULLY home into the new push fit connectors, the pipes should go
almost in as far as the swage on the plastic pipe. Give them a small tug
to ensure they don't just pull out and are fully locked home.

Go back to the compressor assy and
reconnect the 2 pipes you disconnected earlier, but leave the cover off
for now so you can test for leaks.

NOTE!!.. TAKE EXTREME CARE TO NOT CROSS THREAD THE PIPES
IN THE VALVE ASSY AND DO NOT OVER TIGHTEN THEM!!!

Now, open the drivers door window,
shut the door and make sure ALL other doors are closed, start the vehicle
and the compressor should start to run straight away, allow it to run for
about 15 secs, by this time the bags should have started to take "normal"
shape. STOP the engine and check to see there is no twists or creases in
the bags and they are inflating "neatly".

If all is good, restart the car and
allow the compressor to run its full cycle to inflate the bags up to
working pressure. Once it has stopped, refit
the road wheels, you may have to adjust the axle height by using the 2
jacks to allow the wheels to be refitted.

Once you have put the wheels back on,
release the load on the 2 axles jacks so the rear axle is on the wheels
again, you may hear the system release air etc, this is due to the fact
your moving the height sensors up or down whilst lowering the jacks. Once
the wheels are on the floor, remove the 2 jacks from under the car
completely and restart the car and leave it idling.

Whilst the vehicle is idling away,
jack it up and remove the axle stands from under the chassis, each time
you remove one, CAREFULLY lower it down on to its own weight as the air
springs may still NOT be at full working pressure. Do the same both sides.
Once its fully down and off the axle stands, it may still be sitting lower
than normal, but this will soon sort itself out once the car has got is
bearings ref the pressure / height sensor settings.

Once the vehicle is back to "normal"
height, press the offroad switch and check to see the rear raises up the
extra 2 inches. Once its up, have a good look / listen / feel for leaks at
the new pipe fittings and at the 2 pipes on the compressor assy that you
removed earlier. If all is good, refit the compressor assy cover, remove
the wheel chocks, and take the vehicle for a test drive. It should lower
itself back to normal height once you go over 20 mph.

That's it Job done!!!

NOTES.

Up until the cold weather, I never had a
single issue, I can only put this down to coincidence, or the fact that
the cold weather means the rubber on the air springs is less flexible at
lower temperatures, therefore its ability to "self seal" is reduced
significantly and they leak easier

My car DEF feels better on new springs
as the new rubber is most likely not as "worn" as the old tired air
springs.

The Vehicle now raises and lowers a LOT
quicker when using the offroad switch, this maybe due to the leak that was
present, but also maybe due to the fact the new spring rubber is not as
stretched / flexible / old as the old units, so it takes less air to
inflate them to the required height.

When washing the car, I periodically
raise the rear on the offroad switch, and then wash / clean around the
lower parts of the air bags where they "roll over" themselves. This I hope
will help keep them clean and longer lasting. This I would suggest is more
important if you use the vehicle offroad in mud etc.